Blankenship, J. T. | bioRxiv Science

bioRxiv2026

ER shaping proteins guide spindle elongation and division during rapid cleavage mitoses

The ER is a complex network of membranes that inhabits much of the cytoplasm of cells - however, this network undergoes a massive condensation and rapid remodeling during cell division. In Drosophila cleavage divisions, this results in a tight association of the ER with centrosomes and mitotic spindle poles. Previous work has shown that this relationship between the ER and centrosomes must be finely tuned to enable successful spindle elongation, and that overaccumulation of the ER in these stages can result in failed centrosome maturation. During interphase, the ER exists in tubular and sheet-like arrangements, with a variety of "shaping" proteins enforcing these topologies. Here, we examine the contributions of these ER shaping proteins to the rapid changes that occur during cleavage mitoses in the Drosophila embryo. A screen of ER shaping proteins revealed that disruption of Reep-family proteins leads to mitotic failures at characteristic cleavage stages. Compromising ReepA, the Drosophila ortholog of the Reep1-4 subfamily, had a lesser impact on early embryonic mitoses. However, ReepB (the ortholog of the Reep5-6 subfamily) disruption, significantly affects ER mitotic coat morphologies, resulting in a frilled ER phenotype and a reduction of ER adherence to the spindle space accompanied by division failures. Overexpressing ReepA does not rescue ReepB mitotic or ER morphology defects and instead introduces local condensates of abnormal ER structures. These data suggest that dedicated Reep proteins guide ER mitotic properties at specific early developmental stages. Using a cell-based in vitro analysis of Drosophila Reeps, we identify differential "tubulating" properties of ReepA and ReepB. Together these data suggest that the minutes-scale ER remodeling required for early mitoses is governed by shaping proteins, and that ReepB family members are especially important in some of the most rapid cleavage divisions that occur in early embryo.

cell biology↗

bioRxiv2020

Vps54 regulates Drosophila neuromuscular junction development and controls postsynaptic density composition via a Rab7-dependent mechanism

Vps54 is a subunit of the Golgi-associated retrograde protein (GARP) complex, which is involved in tethering endosome-derived vesicles to the trans-Golgi network (TGN). In the wobbler mouse, a model for human motor neuron (MN) disease, reduction in the levels of Vps54 causes neurodegeneration. However, it is unclear how disruption of GARP-mediated vesicle transport leads to MN dysfunction and ultimately neurodegeneration. To better understand the role of Vps54 in MNs, we have disrupted expression of the Vps54 ortholog in Drosophila and examined the impact on the larval neuromuscular junction (NMJ). Here, we show that both null mutants and MN-specific knockdown of Vps54 leads to NMJ overgrowth. Reduction of Vps54 partially disrupts localization of the t-SNARE, Syntaxin-16, to the TGN but has no impact on endosomal pools. Presynaptic knockdown of Vps54 in MNs combined with overexpression of the small GTPases Rab5, Rab7, or Rab11 suppresses the Vps54 NMJ phenotype. Conversely, knockdown of Vps54 combined with overexpression of dominant negative Rab7 causes axonal and behavioral abnormalities including a decrease in postysynaptic Dlg and GluRIIB levels without any effect on GluRIIA. Taken together, these data suggest that Vps54 controls larval MN axon development and postsynaptic density composition by modulating Rab7-mediated endosomal trafficking.

neuroscience↗